Molly
cycloidal pump



March 30, 1965 MOLLY 3,175,504

CYCLOIDAL PUMP Filed Feb. 13, 1963 2 Sheets-Sheet l INVENTOR.

United States Patent 3,175,504 CYCLOIDAL PUMP Hans Molly, 48 Dr. Eugen-Essig-Strasse, Malsch, near Karlsruhe, Germany Filed Feb. 13, 1963, Ser. No. 258,306 Claims priority, applifitigg Gelrmany, Feb. 16, 1962,

4 Claims. ci. 103-130 on the opposite side thereof. With known pumps of this type, the pinion is keyed to the driving shaft which is rotating eccentrically relatively to an internal ring gear in the casing. On each rotation of the shaft the ring gear is rotated further by one width of tooth relative to the shaft. Between the internal teeth of the ring gear and the teeth of the pinion chambers are provided which on the one side of the plane defined by the central axes of the ring gear and the driving shaft continually increase in size and on the other side of such plane continually decrease in size. If a controlling slide valve is provided connecting the chambers on the one side with a suction line and on the other side with a pressure line, the rotation of the shaft causes fluid to be drawn from the suction line and fed to the pressure line. The pressures obtainable with a pump of this type presently depend on the tightness of engagement between the teeth of the ring gear and that of the pinion. Since thisinvolves a positive guide of the pinion in the ring gear, this tightness is dependent on the accuracy of the fit. Now, the pinion is additionally mounted on the driving shaft so that a kinematic redundance of determination exists which might lead to jammings if the tolerances provided are not relatively great. A further difliculty stems from the fact that with known cycloidal pumps the pinion is rotating with the full driving speed since it is carried along with the driving shaft, being keyed thereto. Therefore, it rolls about the internal teeth with a relatively high peripheral speed leading to considerable strain on the parts.

For this reason, cycloidal pumps of the type described, despite various favorable properties have only been in practical use to a limited extent and have been applied only under conditions where particularly high pressures are not of much importance. By way of example, such a pump has been proposed as filling pump for hydrostatic axial piston transmissions.

It is the object of the present invention to design a cycloidal pump of the aforementioned type so as to avoid this kinematic redundance of determination and so that the relative movement between the pinion and the ring gear takes place with less peripheral speed.

According to the invention this object is being attained by providing that the pinion is freely rotatably supported on an eccentric hoop, with the ring gear being stationary. The hoop in turn is eccentrically and rotatably supported on an internal eccentric rotating about the center of the ring gear in such a manner that the eccentric hoop executes a circular movement about the center point of the ring gear and causes the pinion to roll thereat. In this arrangement, the double-eccentric support of the pinion permits an alignment of the pinion relative to the ring gear. An additional degree of freedom is provided, thereby avoiding the possiibility of redundance of determination and of jamming. In accordance with the rolling in the ring gear the pinion may rather freely adjust or let vary its eccentric point, without being disturbed from the side of the drive axis. Besides, the high rates of relative peripheral speed are dispensed with, being replaced by the eccentric movement which has only a very small path.

An embodiment of the invention is presented in the drawings and described as follows:

FIG. 1 is a perspective view of a pump of the invention, wherein some parts are shown broken away.

FIG. 2 is a cross-sectional view and FIG. 3 a longitudinal sectional view of the pump.

FIG. 4 is a perspective view of the eccentric hoop and FIGS. 5 and 6 illustrate the kinematic conditions and those of forces in the pump of the invention.

Reference numeral 1 designates an external rim defining a ring gear stationarily arranged in the casing 1. Ring gear 1 is provided with internal teeth 2 formed with curve-shaped teeth. A gear or pinion 3 engages the teeth of ring gear 1 with the center of the pinion orbiting about the center of the ring gear. The teeth spaces of the pinion correspond in shape to the teeth 2 of the ring gear, and the teeth of the pinion substantially correspond to the teeth spaces of the ring gear so that the pinion and ring gear will snugly engage each other. The number of teeth of pinion 3 is one less than that of ring gear 1. The teeth are so designed that pinion 3 is in meshing engagement with the internal teeth 2 at a point 4, whereas the teeth of the ring gear and pinion touch head to head at another point 5. Thus, pinion 3 is completely positively guided in the internal teeth 2. On movement of pinion 3 about the internal teeth 2 a small shift of pinion 3 is effected. When the center of pinion 3 has made one orbit about the center of ring gear 1, the pinion is shifted by one tooth width. In the embodiment described the ratio of the number of teeth is 13:14. Consequently, pinion 3 has made one full turn after its center has orbited about the center of the ring gear 2 thirteen times. Pinion 3 is mounted on an eccentric hoop 6. Hoop 6 has a central opening 7 defining a circular inner surface 7' formed about an axis 7" which (FIG. 4) is arranged eccentrically to a circular outside surface 8 thereof upon which gear 3 is mounted. With this central opening 7 the hoop 6 is mounted on an eccentric 9 which rotates about an axis 10. Eccentric 9 has an axis 9" which corresponds to axis 7" of opening 7. Note in FIG. 1, that the eccentric 9 is arranged on a hollow shaft 12 being formed with a cylindrical insertion 11 at the inside thereof. This hollow shaft 12 is carried along with a driving shaft by means of splines 13 and journaled in casing 1' in a ball bearing 12'. Laterally, the pump chambers are sealed by annular bodies 14, 15.

Pinion 3 is formed with radial bores 16 between all teeth (FIG. 2). The eccentric hoop 6 possesses crescent shaped recesses 17, 18 so that the surface 8 provides a controlling slide valve in which the bores 16 terminate. The recess 17 communicates with an annular chamber 20 through axial bores 19 (FIG. 4), which chamber connects to a fluid inlet 20 of easing 1' and wherefrom the fluid shall be sucked in. The recess 17 therefore provides the suction side of the controlling slide valve. Recess 18 connects to a crescent shaped recess 22 of the internal eccentric 9 through radial bores 21. This again connects to a central fluid outlet channel or chamber 23 While on the left side thereof they increase in size. Therefore, fluid is sucked into the left chambers whereas the fluid is forced out of the right chambers. Note, that the expressions right and left refer to the. existing condi- .tion illustrated in- FIG, 2.. The plane A-A is rotating with the eccentric 9 and the'eccentric hoop 6. With this plane A-A the controlling slide valve is also rotating being provided by'theeccentric hoop 6. Therefore, the recess 17 always connects to the chambers increasing in volume, through the channels 16, whereas the recess 18 always connects to the chambers decreasing in size. Therefore, oil or other fluid is sucked in through the openings or channels 19 from chamber 20'into the recess 17 and the left chambers on the suction side. Upon further rotation of the eccentrics 9, 6 suchfluid, e.g., oil is forced into the recess 18, then inwardly through channels 21, recess 22 and channels 23 and out through the outlet channel 23'. r

The two eccentrics and 6 have the same effect as a crank, as is illustrated in FIG. or 6, itbeing imagined that the crank 9"is' driven in the direction of the arrow 27 and the pinion 3 is supported as at '8'. The axis 9" of the eccentric corresponds'to the axis 7 of the central opening 7 of hoop 61 It can be seen that the distance a is variable so that the pinion obtains an additional degree of freedom. It may therefore adapt to the internal teeth of the ring gear, without its support on the double'eccentric 6, 9 interferingin someway.

If there were no friction existing, the eccentrics 9 and 6 wouldbe favorably designed as to lead to the conditions illustrated inFIG. 5; The oil pressure on the pressure side of the controlling slide'valve (recess 18) exercisesia; force P perpendicularly to plane AA, that is to say, perpendicularly to the p'lane A-A through the central axis 25 of ring gear 1 (which corresponds to the axis of rotation of the eccentric 9) and the central axis 26 of the outside surface 8 eccentric hoop 6 (which corresponds to the central axis 8 of gear 3). The, friction being negligible this force P would, in the arrangement accordingto FIG. 5, align with the longitudinal dimension of lever 6'. V

Different conditions prevail if the friction must be taken into consideration. On rotation of the eccentric in clockwise direction (arrow 27), the :friction exercises a force P which produces a torque in counterclockwise di- Y rection and being proportional to the contact pressure P. .With such force the-teeth would be pressed head'on head in point 5 (FIGLZ) with an arrangement accordin'g'to FIG-5. Even though a certain contact pressure between the teeth in point 5 is desirable so as to obtain a good sealing between pressure and suction side, undesirable wear mighhhowever, occur with excess of contact pressure. In FIG. 6 the lever 6' is therefore somewhat inclined relatively to plane A-A so that the lines of connection of the center points of internal teeth 2 andeccentric'hoop 6 on the one hand (25 and 8' respectively) and of eccent-ric hoop and internal eccentric on the other hand (8' and '9" respectively) constitutean obtuse angle 30. Thereby, it is achieved that the resultant R of P and P'again aligns with the longitudinal dimensionof' lever 6'. In such case,'no contact pressure would occur; Ofcourse,

through adequate inclination of lever 6' a certain contact pressure between the teeth may be maintained. If desired, it may also be possible to make the lever 6' incline to the other side so as to. achieve a particularly 4 strong contact pressure between pinion 3 and internal teeth 2.

For the purpose of balancing the eccentric pinion 3 the eccentric hoop 6 is provided with extensions 28 (FIGS. 3 and 4) on one side.

I claim:

1. In an internal gear machine having a stationary ring gear with a given number of internal teeth concentric with a first axis, a rotatable pinion having one less than said number of teeth to mesh with those of the ring gear, said pinion being adapted to orbit about said axis with its teeth in meshing engagement with the internal teeth at oneside andtouching head to head on the other side, said. pinion having. a central opening concentric withthe axis of the. teeth thereof, and a shaft extending through said opening and mounted'for rotation concentric with the first axis, the improvement comprising: said shaft having an eccentric fixed thereto with a cylindrical outer face eccentric to'the first axis; and a hoop between said eccentric and said pinion and rotatable with respect to each, said hoop having an outersurface formed about one axis and an inner. surface formed about an other axis, said inner surface being in supporting contact with the eccentric face and said outer surface being in supporting contact with the interior of said pinion at said opening, whereby the pinion is provided with an additional degree'of freedom to better enable it to. provide said head to head contact at said other side in a fiuid sealing manner while engaging. the ring gear at said one side.

2. In a machine as setforth in claim 1, the improvement comprising: said pinion having bores extending radially betweensaid teeth-thereof to the inner opening therein, said hoop havingconforrnations about the exterior thereof defining. a controlling slide valve.

3. In a machine as set forth in claim 2, wherein said conformations define two crescent shaped peripheral recesses on the-hoop, said hoop having a radial bore cornrnunicating with one of the recesses, said eccentric having a radialbore and passageway means communicating with the hoop bore ata given position of. the hoop on the eccentric.

4.1An internal gear pump including: a stationary ring gear with a given number of internal teeth concentric with a first axis; arotatable pinion having one less than said numbernof teeth to mesh with those of the ring gear, said pinion having teeth and being adapted toorbit about said axis withits teeth in meshing engagement with the internal teeth at one side and touching head to head on the other side, a central opening in said pinion defining a bearing facesand boresinsaid pinion extending from between the teeth to the central opening; a hoop within said opening, said .hoop having a circular outer surface and a circular. inner surface formed about spaced axes, said outer surface being in supporting contact with said bear- 7 ing face to rotatably support the pinion on the hoop, said 'hoop'having two crescent recesses in the outer surface, said recessesbeingspaced circumferentially with each other and inalignment with the inner ends of said bores, said hoop having fluid channels extending from said recesses,

V shaft means including an inner eccentric secured thereto,

said eccentric being within said hoop and'in contact with saidinner surface to rotatably support the hoop thereon; and casing means about said ring'gear and fixedlysupporting said ring gear and rot'atably supporting s'aid shaft means, said meansdefiningan inlet chamber positioned to communicate with some of said channels at one rotational position of the hoopand adischarge chamber positioned at another rotational position o'f'the hoop to communicate with others of said channels of the hoop, whereby as said shaft is rotated said eccentric and hoop cause said pinion to orbit about the ring gear and said hoop provides said pinion with an additional degree of freedom and serves'as a slide valve to connect the spaces between the teeth. of the ring gear and pinion at one side to said to said discharge chamber.

5 6 inlet chamber and to connect said spaces at the other side FOREIGN PATENTS 55 6,217 8/32 Germany.

References Cited by the Examiner 882,805 7/53 Germany.

UNITED STATES PATENTS 9,359 1915 Great EJ118111. Bowser 230 145 5 262,132 7/27 Great Britain. Heinrich 350,071 6/31 Great Bruam.

Carrey 230145 B E matte et a1. M 91*56 JOSEPH H. RANSON, IR., Primary xamlner. Patin 230-145 10 WILBUR J. GOODLIN, Examiner. Dettlof et a1 103-13O 

1. IN A INTERNAL GEAR MACHINE HAVING A STATIONARY RING GEAR WITH A GIVEN NUMBER OF INTERNAL TEETH CONCENTRIC WITH A FIRST AXIS, A ROTATABLE PINION HAVING ONE LESS THAN SAID NUMBER OF TEETH TO MESH WITH THOSE OF THE RING GEAR, SAID PINION BEING ADAPTED TO ORBIT ABOUT SAID AXIS WITH ITS TEETH IN MESHING ENGAGEMENT WITH THE INTERNAL TEETH AT ONE SIDE AND TOUCHING HEAD TO HEAD ON THE OTHER SIDE, SAID PINION HAVING A CENTRAL OPENING CONCENTRIC WITH THE AXIS OF THE TEETH THEREOF, AND A SHAFT EXTENDING THROUGH SAID OPENING AND MOUNTED FOR ROTATION CONCENTRIC WITH THE FIRST AXIS, THE IMPROVEMENT COMPRISING: SAID SHAFT HAVING AN ECCENTRIC FIXED THERETO WITH A CYLINDRICAL OUTER FACE ECCENTRIC TO THE FIRST AXIS; AND A HOOP BETWEEN SAID ECCENTRIC AND SAID PINION AND ROTATABLE WITH RESPECT TO EACH, SAID HOOP HAVING AN OUTER SURFACE FROMED ABOUT ONE AXIS AND AN INNER SURFACE FORMED ABOUT ANOTHER AXIS, SAID INNER SURFACE BEING IN SUPPORTING CONTACT WITH THE ECCENTRIC FACE AND SAID OUTER SURFACE BEING IN SUPPORTING CONTACT WITH THE INTERIOR OF SAID PINION AT SAID OPENING, WHEREBY THE PINION IS PROVIDED WITH AN ADDITIONAL DEGREE OF FREEDOM TO BETTER ENABLE IT TO PROVIDE SAID HEAD TO HEAD CONTACT AT SAID OTHER SIDE IN A FLUID SEALING MANNER WHILE ENGAGING THE RING GEAR AT SAID ONE SIDE. 